Slag pot carrier

ABSTRACT

An improved slag pot load carrier is provided. Fluid powered means are included to assist the primary dump mechanism in moving a vehicle load pivoted on the main vehicle frame from a carry to a dump position, and to return the load to its carry position. Suspension means are provided to lower and raise at least a portion of the vehicle frame and to resiliently support the frame against shocks. A hydro-pneumatic system is also provided to appropriately actuate the suspension means, and the primary dump and return assist mechanisms.

nited States Patent 1191 Kress [45] July 23, 1974 SLAG POT CARRIER3,506,148 4/1970 Vik 214/314 [76] Inventor: Edward S. Kress, PO. Box368,

Brimfield L 61517 Primary Examiner-Robert J. Spar AssistantExaminer-Lawrence J. Oresky Flledl g- 197,2 Attorney, Agent, orFirm-Wolfe, Hubbard, Leydig, 21 Appl. No.2 282,728 & 05am 62 i RelatedU.S. Application Data [57] ABSTRACT 5 2 5 22? 1970 An improved slag potload carrier is provided. Fluid powered means are included to assist theprimary 52 U.S. c1. 214/313 267/64 R dump mechanism "10mg a vehiclePivoted 51 11111. C] 865!) 21/02 the main Vehicle frame fmm a carry adump [58] Field of Search u 214/312 313 314 tion', and to return theload to its carry position. Sus- 1 g i 267764 pension means are providedto lower and raise at least a portion of the vehicle frame and toresiliently sup- [56] References Cited port the frame against shocks. Ahydro-pneumatic system is also provided to appropriately actuate thesus- UNITED STATES PATENTS pension means, and the primary dump andreturn as- 3,330,429 7/1967 Kress 214/314 i' h i 3,335,885 8/1967Livingston 214/314 4 3,365,191 1/1968 Ellis, Jr. et al. 267/64 R 4Claims, 17 Drawing Figures l pmgm nJuLzsm sum Olaf-w 3,825,135

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3.8251135; sum as M w Pmmiumzalm PATENTEDJULZBW awazmss sum 02 or wPATENTEDJuL23197-4 sum 10 0? 1o SLAG POT CARRIER This application is adivision of my application Serial No. 98,306, filed Dec. l5, 1970, nowUS. Pat. No. 3,722,874 issued Mar. 27, l973.

This invention relates generally to mechanisms for transporting andmanipulating heavy loads and more particularly concerns improvements intransporter vehicles for lifting, supporting, carrying and dumping heavyloads. This transporter vehicle may be of the general type disclosed inUS. Pat. No. 3,330,429.

For purposes of illustration, there is shown a vehicle fork carrying aload comprising a ladle or pot of the kind used in the steel makingindustry. The slag pot may weigh more than 200 tons and may bev filledwith molten slag and steel from a steel furnace. A large and heavycontainer filled with a great quantity of molten materialof this type isdifficult to handle.

It is the general aim of this invention to provide an improved vehiclehaving facilities for handling a load such as a slag pot or any bulkheavy material container. It is a related object to provide an improvedfluid power system for such a carrier vehicle which will allow thevehicle to easily pick up, carry, dump, return and disengage its load.

It is another object of the invention to provide a slag pot dump andreturn assist system for assisting a powered main dump system in tiltingthe heavy vehicle load from a carry to a dump position, and in returningthe loadfrom the dump to the carry position;

It is an associated object to provide a dump or return assist system toassist the main dump cylinders of a transporter in rotating a load suchas a slag pot to and from a dump position when the main cylinders andload are located in relative positions such that the load cannot beeasily rotated by the main dump cylinders alone.

It is another object of the invention to provide a vehision systemforcarrying heavy loads such as slag pots and the like which willallow'sufficient play or movement within the suspension system to avoidsevere shocks being transmitted to and from the vehicle and load by thevehicle wheels and yet which will avoid excessive bounce or travelwithin the system.

It is another object of the invention to provide a vehi'- cle suspensionunit which will produce a smooth vehicle ride and a low rate of bounceor low spring rate.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings in which:

FIG. 1 is an overall-side elevational view of a typical vehicle forcarrying heavy loads such as slag pots in which an embodiment of theinvention is utilized;

FIG. 2 is an overall plan view of the vehicle;

FIG. 3 is a fragmentary side elevational view of the trailer portionshown of the vehicle illustrated in FIGS. 1 and '2 with the associatedload or pot resting on ground; v

FIG. 4 is an elevational end view taken substantially in the plane ofline 4-4 in FIG. 3 showing in further 2 detail the rear of the vehicletrailer and embodiments of the invention;

FIG. 5 is a fragmentary view taken substantially in the plane of line5-5 in FIG. 2 and showing in further detail the dump and return assistsystem with the cable taunt at the inception of tilt; 3

FIG. 6 is a fragmentary sectional view similar to FIG. 5 and takensubstantially in the plane of line 5-5 in FIG. 2 but showing the potnear the end of the dump assist position;

FIG. 7 is a fragmentary sectional view similar to FIGS. 5 and 6,.takensubstantially in the plane of line 5-5 in FIG. 2 and showing the slagpot load in an intermidpoint tilt position;

FIG. 8 is a fragmentary sectional view similar to FIGS. 5-7 takensubstantially in the plane of line 5-5 in FIG. 2 showing the slag potload in its dumped position;

FIG. 9 is a fragmentary sectional view similar to FIGS. 5-8 takensubstantially in the plane of line 5-5 in FIG. 2 showing the slag potload as it is being returned from the dump position to the carryposition by the return assist system;

FIG. 10 is a fragmentary plan view showing the power cylinder andassociated assist system apparatus;

the plane of line 12-12 in FIG. 1 showing in further detail the cables,dump body standards, and other parts of the vehicle;

FIG. 13 is a sectional view taken substantially in the plane of line13-13 in FIG. 3 showing in further detail the suspension cylinderportion of the invention as it appears in a partially extended position;7

FIG. 14 is a sectional view taken substantially in the plane of line14-14 in FIG. 1 and showing in further detail the suspension system ofthe invention as it appears in the most fully extended position;

FIG. 15 is a sectional view taken substantially in the plane of line13-13 in FIG. 3 showing a modified version of the suspension cylinderportion of the invention in a partially extended position;

FIG. 16 is a sectional view taken substantially in the plane of line14-14 in FIG. 1 showing the modified version of the suspension cylinderin the most fully extended position, and

FIG. 17 is a schematic view illustrating the hydraulic system utilizedin connection with the illustrated embodiment of the invention.

While the invention will be described in connection with a preferredembodiment, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications and equivalents as may be includedwithin the spirit and scope of the invention.

Turning first to FIGS. 1-4, there is shown a typical rubbertired carriervehicle 20 upon which an embodiment of the invention may be installed.The vehicle 20.

. includes a drive unit 21 having two driving wheels 22 goose neck 26and arigid, generally U-shaped frame 27, the frame 27 being defined by across beam 28 and a pair of rearwardly extending arms 29 which generallyembrace the vehicle load. In the illustrated vehicle, the load may beconsidered to be a large slag furnace pot P. This pot P may be filledwith molten slag from a slag furnace and may weigh on the order of 200tons. The pot P is selectively engaged and secured to the trailer 24 bya pot-engaging hook mechanism 31.

Ground engaging trailer wheel sets 33 are mounted at each side of thetrailer 24. Each wheel set 33 is mounted on an axle 35 which is securedto the trailing end of a wheel support arm 36. The forward end of thesupport arm 36 carries a pin 37 which is pivoted on lugs 39 extendingdownwardly from the frame arms 27. The pivoted mounting of the pin 37provides the required swinging and sliding connection between the wheelsupport arm 36 and the frame arm 29.

In the illustrated vehicle, the pot P is surrounded by a cradle frame 41for carrying the pot P upon the engaging hook mechanism 31. To allowrotation of the cradle frame 41 and pot P from a carry position P-l to adump position P-4 (shown in phantom lines FIG. 1), the cradle frame 41is pivoted upon the trailer frame 27 by pivot connections 43 providedbetween the cradle frame 41 and the trailer arms 29. It will beunderstood that while a slag pot is illustrated as the vehicle load, thevehicle and invention can be used in association with a number ofdifferent containers and loads.

For rotating the slag pot P from its carry position P-l to its dumpposition P-4, primary or main power means here illustrated as fluidpower cylinders 45 are provided. The illustrated cylinders 45 arejournalled upon the trailer arms 29 by means of collars 46; piston rods47 of the cylinders 45 are pivotally connected to the cradle frame 41 atpin connections 48, as may be particularly seen in FIGS. -9.

Owing to the location of the cylinders 45 relative to the pot P and thepivot connections 43, the geometry of the movements of these parts maymake it difficult for the cylinders 45 to move the pot P into all of thepositions required in rotating the pot P from a carry position P-lthrough an arc to a dump position P-4 and returning the pot to its carryposition P-l. More specifically, it will be noted that in the embodimentillustrated, the force exerted by the primary cylinders 45 acts torotate the pot P through a relatively short lever arm when the pot is ina carry position P-l or a dump position P-4. In accordance with oneaspect of the invention, therefore, assist means are provided to assistin rotating the pot P from its carry position P-l to its dump positionP-4.

In the illustrated embodiment of the invention, assist means includes anassist power means 50, and flexible, tensible link means, hereillustrated as a cable 51 connected at one point 52 to the assist powermeans 50 and at the other point 53 to the dump body or tilt frame 41.

The cable 51 is trained beneath cable reaction structures or extensions54 which depend from the tilt frame 41. The extensions 54 allow thecable 51 to be sufficiently long that the cable does not unduly strainthe power means 50 when the pot is being dumped (see FIG. 7), and yetthe slack in the cable is effectively taken out for the initial liftingaxis action (see FIGS. 5 and 6).

To assist in lifting the pot through its vertical arc of rotation fromthe carry position p-l to the dump position p-4, in the illustratedembodiment of the invention, the cable 51 is connected to the assistpower mechanism 50 at a point located above the pivot 43 of the pot P.The second connection point 53 is located on the dump body frame 41 at aspot between the pot pivot point 43 and the assist power means 50. Itwill be understood that other connection locations may be used withoutdeparting from the scope of the invention, but the described arrangementis simple yet effective.

It is a feature of the invention that the requisite lifting andwithdrawing motion of the first connection point 52 of the cable 51 isprovided by the assist power means 50 illustrated in FIGS. 10, l1 andelsewhere. The assist power means 50 includes a fluid power cylinder 56pivotally attached near its cylinder rod end 57 to the goose neck 26. Alifting lever 58, also pivotally attached to the goose neck 26 at ajournal 59, is attached at its opposite end to the first connectionpoint 52 of the cable 51. To provide the appropriate swinging arc oftravel for the end of 60 of the lifting lever 58, the fluid powercylinder 56 is attached to the lever 58 at a point 61 intermediate theends 59 and 60 of the lever 58. A stop mount 62 is provided to limit thedownward rotation of the lever 58 and to avoid jamming the mechanism byaccidentally substantially aligning the thrust axis of the cylinder 56with the chord of the lever 58.

As may be seen in FIGS. l0, l2 and elsewhere, the

.tensible link means includes a single cable attached, at

each of its ends, to the cradle frame 41 and having a mid-portion 64passing through a pulley attachment 65 connected to the free end 60 ofthe lever 58. Such arrangement allows, in further accordance with theinvention, automatic equalization of the tension upon the cable spans asthe load is lifted. Such equalization of tension, in turn, producesequal lengths of cable engaged with the pot between the connectionpoints 52 and 53, thereby eliminating any tendency to misalign theassist lifting means and to accidentally lift one side of the pot higheror more rapidly than the opposite side.

Another function of the cable 51 is to limit the rota tion of the pot Pas it may be tilted past its fully dumped position P-4, normally definedby a dumping pad, thereby protecting the primary dump cylinder 45 fromoverextension and consequent damage. To protect, in turn, the cable 51,a biasing means such as a spring 66 acts as a snubbing device togradually tension the cable 51 when the pot P is moved into suchover-tilted position.

Operation of the vehicle dump mechanism may now be easily envisionedfrom the above description, and from particular reference to FIGS. 5-9.When it is desired to rotate the pot P from its carry position P-l toits dump position P-4, the operator actuates appropriate hydrauliccircuitry for the extension of the piston rods 47 in the primary liftcylinders 56. As the assist power cylinder 56 is extended, the end 60 ofthe rotating lever 58 is moved through an upward and outward arc,thereby drawing the cable 51 generally upwardly. Such motion of thecable 51 urges the extensions 54, tilt frame 41, and pot P to rotateabout the pivot point 43, thereby rotating the pot into a preliminarilyrotated position P-2.

Before the pot reaches a top dead center position P-3, the standards 54are, as illustrated, disengaged from the cables 51. Continued extensionof the main piston rods 47 alone causes, as may be seen in FIG. 8, thepot to rotate to its fully dumped position P-4. Appropriate hydrauliccircuitry allows the assist power means 56 to reverse its motion andretract during the described latter portion of the dump cycle, as thepot moves from its top-most position P-3 to its fully dumped positionP-4J This retraction allows the lift lever cable end 60 to rotate towardthe pot P and permits the pot P to rotate to its fully dumped positionP-4 without breaking or stretching the cable 51.

When it is desired to return the pot from its fully dumped position P4to its carry position P-1, and the main lift cylinders 45 are actuatedso as to retract the main piston rods 47, the assist power means 56 areagain actuated in an extending direction. The cable 51 is therebytensioned, and the tilt frame 41 and carried pot P are pulled toward thecarry position. At the top dead center point P-3 in the return cycle,assist power means 56 is once again allowed to retract, thereby allowingsubsequent motion of the cable toward the now descending pot P so as tocradle the extensions 54 by the cable 51 and gently lower the pot intoits carry positron. m

For carrying the vehicle load and resiliently supporting it againstshocks encountered as the vehicle travels over an uneven surface inaccordance with another aspect of the invention, suspension cylinders 80are provided upon each side of the vehicle, as may be seen in FIGS. 1and 2.

In the illustrated embodiment particularly seen in FIGS. 13 and 14, thesuspension cylinders 80 include a first or outer hollow cylinder 81having a wall 82 open at one end 83 and closed, as by a cap 84 andthreaded collar 85 at the opposite end. This outer cylinder 81 issecured by appropriate structure to the supported or suspended portionsof the frame; in the embodied illustration, the frame arms 29 areattached to the outer cylinder 81.

Carried for sliding motion within the first cylinder 81 is a hollowsecond cylinder 88 closed at both ends. Between the first and secondcylinders is thus created a first fluid chamber A. To limit the travelof the second cylinder 88 with respect to the first cylinder 81, anannular stop 89 is provided upon the outside of the second cylinder forengagement with annular stop 90 fixed upon the inside of the firstcylinder 81.

Carried at the bottom closed end 92 of the second cylinder 88, is a balljoint 93 for connection to the trail arms 36 which are, in turn,directly connected to the wheel axles 35 and wheel sets 33. Thus, itwill be seen that the ball joint 93 and closed end 92 of the secondcylinder 88 respond to motion imparted to the wheel sets 33 by thetravel of the vehicle over the ground surface, while the first cylinder81 responds to the motion of the vehicle load and frame arms 29.

Carried within the second cylinder 88 is a floating piston 95 fordividing the interior of the second cylinder 88 into two additionalfluid compartments B and C. Chambers A and B are filled with arelatively incompressible fluid, such as hydraulic fluid, as through aninlet port 96. The third chamber C is filled with a predetermined staticamount of relatively compressible fluid. Such fluid may take the form ofcompressed air or nitrogen in the illustrated embodiment.

To provide fluid communication between the first fluid compartment A andthe second fluid compartment B, there is provided a damper valve 97.

This damper valve 97 is of such construction as to allow fluid to passmore rapidly from the first chamber A to the second chamber B thanpasses from the second chamber B to the first chamber A under identicalabsolute pressure differentials. When, in the illustrated embodiment,fluid pressure is raised in the first chamber relative to that in thesecond chamber, the bored ball 98 is forced away from its seat 99 in thedamper valve, allowing a relatively large quantity of fluid to passthrough the main passage 100 in the damper valve 97. Upon pressureequalization in the chambers, the biasing means 101 urges the bored ball98 back into its seat 99. When the pressure is raised in the secondchamber relative to the first, the bored ball 98 is simply forced moretightly against its seat, and a relatively small amount of fluid isallowed to pass to the small bore 102 within the bored ball 98. Otherconstructions of damper valves providing the described fluid flow may beused without departing from the broad spirit of the invention.

Operation of the suspension system may now be easily understood. When ashock is encountered by the traveling vehicle, the wheels and connectedtrail arms 36 are thrust upwardly toward the trailer frame 29. Suchaction on the part of the trail arms 36 forces the connected secondcylinder further upwardly into the first cylinder, thereby decreasingthe volume of the first fluid chamber A. This action forces therelatively incompressible fluid in the first chamber A rapidly into thesecond chamber B. The increase in volume of fluid within the secondchamber B in turn forces the foating piston 95 relatively downwardwithin the second cylinder 88 against the resilient action of thecompressible fluid carried in the third chamber C.

After the bump or shock has been passed, the suspension systemisreturned to its former condition by the action of the now highlycompressed resilient fluid in the third chamber C against the floatingpiston 95. This compressive action forces fluid from the second chamberback into the first chamber through the damper valve 97 at a relativelyslow rate, thereby relatively slowly returning the system to its normalcondition.

A seal 104 is provided to prevent the leakage of fluid in the firstchamber into the annular space 105 formed between the first and secondcylinders. To further prevent fluid leakage and exclude dirt or otherforeign matter which might otherwise enter the mechanism, second seals106 are provided at the lower end 83 of the first cylinder.

In accordance with another apsect of the invention, selective fluidpower means are provided to positively retract the secondcylinder 88within the first cylinder 81. A port 108 communicates with the annularspace 105 between the cylinder, and may be filled with pressurized fluidwhen desired. Pressure upon the cylinder stop 89 and seal 104 forces thesecond cylinder 88 to retract up into the first cylinder 81. As thevolume of the first chamber A is thus decreased, fluid contained thereinis expelled through the inlet port 96. This retraction system may provehighly useful. For changing vehicle tires, or performing maintenance onthe wheel sets 33, the frame 27 may be blocked in its raised or carryposition or otherwise rendered immobile, and the second cylinder thenretracted. Such retraction raises the wheel support arm 36 and attachedwheel set 33 from the ground. Alternatively, if the frame 27 is notblocked up or otherwise fixed, such relative retractive telescopingmotion of the first and second cylinders will lower the frame through alimited vertical distance. The carried load may thus be set down andthen released by the hook engagement mechanism 31; if specialcircumstances require, an unloaded trailer may also be positivelylowered for engagement with a pot or other load which may be restingupon the ground. After engagement, the trailer frame is raised and thepot or load thus hoisted into the described carry position.

A modified form of the suspension cylinder 110 is shown in FIGS. and 16.Such modified version may find special application in applications wherethe distance between the wheel support structure and the vehicle frameis limited. In this modified version, a first or outer cylinder 111carries within it a second cylinder 112, and a floating piston 113 iscarried within the second cylinder. The top of the first cylinder isconnected, as by a ball joint 114, to a vehicle frame, and the bottom orclosed end of the second cylinder 112 is connected, as by ball joint115, to the wheel-associated structure or trail arms 36. The closed end117 of the second cylinder 112 is so shaped as to accommodate a portionof the length of the ball joint 115 within the cylinder itself, therebydecreasing the overall length of the suspension system. A damper valve118 is located between the first and second fluid chambers for allowingpassage of fluid from the first chamber to the second chamber morerapidly than passage of fluid from the first chamber to the secondchamber under identical absolute pressure differentials.

In accordance with another aspect of the invention, a singlehydro-pneumatic system 130 is provided for operating the main dumpcylinders 45, the assist means 50, and the trailer suspension cylinders80. This system may take the form schematically illustrated in FIG. 17.Valves 131 and 132 are provided for individually controlling each of thesuspension cylinders 80 to allow individual activation or draining ofthe cylinders 80. This individual erection allows one side of thetrailer 24 to be raised higher than the other, thereby canting thetrailer, if necessary, to properly engage a load such'as a pot which maybe resting on an uneven surface. Appropriate actuation of both cylinders80 in tandem allows the load-engaging hook mechanism 31 to be lowered orraised through a limited range of positions, and also provides thedescribed desirable suspension characteristics.

Fluid pressure for operating the primary dump cylinders 45 in tandemtogether with the assist power cylinder 56 to dump the carried load andreturn the vehicle load carrier or port to its carry position isselectively provided through a dump valve 135. Upon operation of themaster valve 135 as shown, pressure is supplied through three fluidoperated pneumatic knocker valves 137, 138 and 139 to extend the dumpcylinder 45 and assist cylinder 56, and move the vehicle load carrier orport from its carry toward its dump position. To retract the load or potto its carry position, the dump valve 135 may be positioned in a retractposition, whereupon the piston rods 47 of the dump cylinders 45 will beforcibly retracted and the assist cylinders are again extended to raisethe load or pot through its top dead center position (see FIG. 7) and toits carry position. It is a feature of the invention that pressurizedfluid is directed as described to the cylinders by a reversible valve140.

In accordance with yet another feature of the invention, the load or potmay be relatively rapidly rotated or dropped from slightly beyond itstop dead center position to its dump position. To this end, a drop valve141 is connected to the knocker valves 137, 138 and 139 provided withinthe reach of the vehicle operator. When the load has moved slightlybeyond its top dead center position, the drop valve may be actuated, andthe knocker valves 137-139 shifted so as to allow the dump cylinders 45and assist cylinder 56 to drain off fluid and the load to drop, by itsown weight, against the pressure of the fluid draining from thecylinders. By alternately operating the load-retract valve and dropvalve before the pot reaches its top dead center position in the retractcycle, the pot may be alternately raised and dropped. Such dropping jarsthe pot and deskulling it of slag or other material which may adherethereto.

I claim:

1. In a carrying and dumping vehicle having a wheeled frame pivoting areceptacle supporting cradle for tilting movement from a supportposition to a receptacle dumping position, the combination comprising,means for selectively moving said wheeled frame vertically to enablesaid cradle to engage and suspend a receptacle, a primary tilting fluidpowered actuator for urging said cradle about said pivot betweensupporting and dumping positions, a power assist assembly including anassist fluid powered actuator on said frame and a link coupling saidassist actuator and said cradle at a point where operation of the assistactuator in one direction tensions said link to initially urge thecradle from either its support position or its dumping position, a fluidsupply system for selectively powering said primary tilting actuator tomove said cradle in either direction, said system including a valve fordriving said assist actuator in said one direction whenever the primaryactuator is driven in either direction.

2. The combination of claim 1 in which said actuators are fluid powered,and including a fluid supply system having selectively operated knockervalves for interconnecting the pressure and exhaust portions of saidactuators and thereby allow a load supported thereby to fall freely.

3. The combination of claim 1 in which said link is flexible cable whichis doubled about a portion of said cradle when the cradle is in supportposition so as to shorten the effective length of said cable whileallowing the cable to unfold and permit the cradle to reach said dumpingposition.

4. In a carrying and dumping vehicle having a wheeled frame pivoting areceptacle supporting cradle for tilting movement from a supportposition to a receptacle dumping position, the combination compris ing,a cradle for engaging and supporting a receptacle, a depending memberrigidly connected to said cradle, means for selectively moving saidwheeled frame vertically to enable said cradle to engage and suspend areceptacle, a primary tilting fluid powered actuator connected betweensaid frame and said cradle for urging said cradle back and forth aboutsaid pivot between supporting and dumping positions, and a power assistassembly including an assist fluid powered actuator on said frame and aflexible link coupling said assist actuator and said cradle saidflexible link extending from 10 flexible link being free of contact withsaid depending member after the cradle is initially urged upwardly andsaid flexible link being free of contact with said depending member uponoperation of the assist actuator in the same direction to tension'saidlink and urge said cradle from its dumping position.

1. In a carrying and dumping vehicle having a wheeled frame pivoting areceptacle supporting cradle for tilting movement from a supportposition to a receptacle dumping position, the combination comprising,means for selectively moving said wheeled frame vertically to enablesaid cradle to engage and suspend a receptacle, a primary tilting fluidpowered actuator for urging said cradle about said pivot betweensupporting and dumping positions, a power assist assembly including anassist fluid powered actuator on said frame and a link coupling saidassist actuator and said cradle at a point where operation of the assistactuator in one direction tensions said link to initially urge thecradle from either its support position or its dumping position, a fluidsupply system for selectively powering said primary tilting actuator tomove said cradle in either direction, said system including a valve fordriving said assist actuator in said one direction whenever the primaryactuator is driven in either direction.
 2. The combination of claim 1 inwhich said actuators are fluid powered, and including a fluid supplysystem having selectively operated knocker valves for interconnectingthe pressure and exhaust portions of said actuators and thereby allow aload supported thereby to fall freely.
 3. The combination of claim 1 inwhich said link is flexible cable which is doubled about a portion ofsaid cradle when the cradle is in support position so as to shorten theeffective length of said cable while allowing the cable to unfold andpermit the cradle to reach said dumping position.
 4. In a carrying anddumping vehicle having a wheeled frame pivoting a receptacLe supportingcradle for tilting movement from a support position to a receptacledumping position, the combination comprising, a cradle for engaging andsupporting a receptacle, a depending member rigidly connected to saidcradle, means for selectively moving said wheeled frame vertically toenable said cradle to engage and suspend a receptacle, a primary tiltingfluid powered actuator connected between said frame and said cradle forurging said cradle back and forth about said pivot between supportingand dumping positions, and a power assist assembly including an assistfluid powered actuator on said frame and a flexible link coupling saidassist actuator and said cradle said flexible link extending from saidassist actuator in a downwardly inclined direction around said dependingmember and being connected to a point on said cradle which lies abovethe lowermost end of said depending member when said cradle is in itssupport position, said flexible link movably engaging said dependingmember on said cradle upon operation of the assist actuator to tensionsaid link and initially urge the cradle upward from its supportposition, said flexible link being free of contact with said dependingmember after the cradle is initially urged upwardly and said flexiblelink being free of contact with said depending member upon operation ofthe assist actuator in the same direction to tension said link and urgesaid cradle from its dumping position.